A broad range of electrical cables and buffered optical fibers cables are installed in modern buildings for a wide variety of uses. These cables are used, for example, to provide data transmission between computers, voice communications, as well as control signal transmission for building security, fire alarms, and temperature control systems. Cable networks extend throughout modern office and industrial buildings, and frequently extend through the space between the dropped ceiling and the floor above.
Ventilation system components are also frequently extended through this space for directing heated and chilled air to the space below the ceiling and also to direct return air exchange. The space between the dropped ceiling and the floor above is commonly referred to as the plenum area. Electrical cables and fiber optic cables extending through plenum areas are governed by special provisions of the National Electric Code (“NEC”).
Because flame and smoke can travel along the extent of a plenum area in the event of electrical fire, the National Fire Protection Association (“NFPA”) developed a standard to reduce the amount of flammable material incorporated into insulated electrical conductors, fiber optic buffers and jacketing of cables. Reducing the amount of flammable material, according to the NFPA, would reduce the potential of insulation, fiber optic buffering, and jacket materials to spread flames and smoke to adjacent plenum areas and potentially to more distant and widespread areas in a building.
In 1975, the NFPA recognized the potential flame and smoke hazards created by burning cables in plenum areas and adopted in the NEC a standard for flame retardant and smoke suppressant cables. This standard, commonly referred to as “the Plenum Cable Standard,” permits the use of a cable without a conduit, so long as the cable exhibits low smoke and flame retardant characteristics. The test method for measuring these characteristics is commonly referred to as the Steiner Tunnel Test. The Steiner Tunnel Test has been adapted for the burning of cables according to the following test protocols: NFPA 262, Underwriters Laboratories (“U.L.”) 910, or Canadian Standards Association (“CSA”) FT-6. The test conditions for each of the U.L. 910 Steiner Tunnel Test, CSA FT-6, and NFPA 262 are: a 300,000 BTU/hour flame is applied for 20 minutes to 24-foot lengths of test cables mounted on a horizontal tray within a tunnel. The criteria for passing the Steiner Tunnel Test are as follows:
Flame Spread Requirement: less than 5 feet
Smoke Generation Requirements:
1. Maximum optical density of smoke less than 0.5
2. Average optical density of smoke less than 0.15 of fire retardant cabling
This standard is one of the most stringent test methods for residential and commercial buildings. In plenum applications for voice and data transmission, electrical conductors and cables should exhibit low smoke evolution, low flame spread, and favorable electrical properties to pass the stringent requirements of copper data cables. Category 5e cables have evolved to provide even higher data transmission speeds with 10 gigabit per second cables, which are now designated Categories (“Cat”) 6, 6e and 6A. A Category 8, or a 40 gigabit per second cable, is being developed. Cables selected for plenum applications must exhibit a balance of properties and every component in a communications cable must perform its role.
Separators, jackets, insulations, buffer tubes and blown fiber tubing used in cables that meet the electrical requirements of Categories 6 and 7 must also pass the new norms for flammability and smoke generation. Tables 2 and 3, below, indicate categories for flame and smoke characteristics and associated test methods as discussed herein.
Fiber optic cables and fiber optic blown tubing, which are used in the plenum areas of buildings, must adhere to the same flame retardancy and low smoke characteristics of the NFPA 262 Plenum Test. Underwriters Laboratory (UL 2885) is a test method for determining whether components or materials of a cable can be designated as a non-halogen cable. Underwriters Laboratory (UL 2885), titled Acid Gas, Acidity and Conductivity of Combusted Materials and Assessment, uses IEC 60754-1, IEC 6074-2 and IEC 62821-1 to benchmark “all materials” within the cable design, i.e., insulation, spline or crosswebs, tapes or other cable fillers, fiber optic buffer and the overall jacket. Based on these test methods, a determination can be made for the presence of halogens, e.g., chlorine, bromine and fluorine. Test protocol 62821-1 Annex B, determines the presence of a halogen using the Sodium Fusion Procedure as described in Part 5.3 IEC 62821-2, i.e., Chemical Test: Determination of Halogens—Elemental Test.
Materials evaluated to IEC 62821-1 Annex B Assessment of Halogens Required for extruded material.
The test protocol consists of the following stages:
Stage 0: Determination of Halogens—elemental test for chlorine, bromine and fluorine using the sodium fusion procedure as described in part 5.3 of IEC 62821-2 (Chemical Test: Determination of Halogens—Elemental Test). If the results for chlorine or bromine or fluorine are positive, proceed to Stage 1.
Stage 1: Test according to 6.2.1 of 60754-2 for pH and Conductivity. If the pH is ≥4.3, the conductivity is >2.5 μS/mm and ≤10 μS/mm, proceed to Stage 2.
Stage 2: Test according to 6.1.1 of 60754-1 for chlorine and bromine content expressed as HCI. If the result if ≤0.5%, proceed to Stage 3.
Stage 3: Test for the determination of low levels of fluorine as described in part 45.2 of IEC 60684-2 (Determination of low levels of fluorine) Methods A (Ion selective electrode method fluoride) or B (Alizarin fluorine blue method).
The European standards have similar goals of fire retardant and low smoke generation cables. Polyvinylchloride, a halogenated material, remains a dominant jacketing grade throughout the European cable community. The standards which have evolved are the so-called International Classification and Flame Test Methodology for Communications Cable. Based on these evolving standards, a new list of acronyms has evolved, albeit with much similarity to the North American standards.
These Euro-classes for cables measure the following:
A.Flame Spread =FSB.Total Heat Release =THRC.Heat Release Rate =HRRD.Fire Growth Rate =FIGRAE.Total Smoke Production =TSPF.Smoke Production Rate =SPR
The European International Classification and Test Methodology for Communication Cables is shown below in Table 1 and it is shown in an abbreviated form.
TABLE 1The European International Classification and Test Methodology forCommunication CablesClassTest MethodsClassification CriteriaAdditional ClassificationAcaEN ISO 1716PCS ≤2.0 MJ/kg (1)Note: Mineral filled circuit integritycableB1caEN 50399 (30 kWFS ≤1.75 m andSmoke production (2, 5) and Flamingflames source)THR1200 ≤10 MJ anddroplets/particles (3) and Acidity (4, 7)andPeak HRR ≤20 kWandFIGRA ≤120 Ws−1EN 60332-1-2H ≤425 mmB2caEN 50399 (20.5 kWFS ≤1.5 m andSmoke production (2, 5) and Flamingflames source)THR1200s ≤15 MJ anddroplets/particles (3) and Acidity (4, 7)andPeak HRR ≤30 kWandFIGRA ≤150 Ws−1EN 60332-1-2H ≤425 mmCcaEN 50399 (20.5 kWFS ≤2.0 m andSmoke production (2, 6) and Flamingflames source)THR1200s ≤30 MJ anddroplets/particles (3) and Acidity (4, 7)andPeak HRR ≤60 kWandFIGRA ≤300 Ws−1EN 60332-1-2H ≤425 mmDcaEN 50399 (20.5 kWTHR1200s ≤70 MJ andSmoke production (2, 6) and Flamingflames source)Peak HRR ≤400 kWdroplets/particles (3) and Acidity (4, 7)andandFIGRA ≤1300 Ws−1EN 60332-1-2H ≤425 mmEcaEN 60332-1-2H ≤425 mmFcaNo Performance Determined
Table 2, below, provides a listing and comparison of the North American standards and the European standards from most stringent flame retardancy and low smoke requirements to least stringent.
TABLE 2A comparison of North American & European Fire PerformanceStandards from most severe to least severe for Communications CablesNorth AmericaNorth AmericanEuropean TestStandardEuropean StandardTest ProtocolsProtocolsMost SeverePlenum TestClass B1Steiner Tunnel -Class B1 30 KWUL 910LAN Comm.88 KWFlame SourcesNFPA 262Cables300 BTU @ 20FS <1.75 m, THR <10 mgFT-6EN 50399-30 KWminutes plusPeak HRR <20 KWCMPEN 60332-1-2smoke peak <.5FIGRA <120 WSAverage <.15SevereRiser TestClass CRiser Test - 154 KWClass C 20.5 KWUL 1666EN 50399-527 KW @ 30Flame SourceFT-410..5 KW &minutesFS <2.0 m TGR <30 m;CMREN60332-1-2Peak HRR <60 KWFIGRA <300 WSLess SevereGeneralClass DGeneral PurposeClass D 20.5 KWPurpose TrayIEC 60332-320.5 KWFlame SourceCable TestEN 50399-70K BIT @ 20THR <70 m;UL 158120.5 KWminutesPEAK HRR <400 KWFT-2/CMFIGRA 1300 WSLeast SevereVW-1Class EBunsen BurnerClass EFT-1IEC 60332-1TestH <425 mm1 minute (15seconds flame)
The use of halogens (e.g. fluoropolymers) in communications cables, such as for insulation materials, crosswebs, tapes, tubes or cable fillers, and the use of low-smoke PVC jacket materials has been widespread in copper based and fiber based cables. Optimizing and meeting the electrical requirements of copper communication cables, i.e., Cat 5e to Cat 6A to Cat 8, without the use of materials comprising halogens, has been the unsolved challenge for over three decades. The materials used for fiber optic buffers and jackets utilize similar halogenated materials to reduce flame spread and smoke generation.
Communication cables conforming to NEC/CEC/IEC requirements are characterized by possessing superior resistance to ignitability, improved resistance to flame spread and lower levels of smoke generation during fires than cables having lower fire ratings. Often these properties can be anticipated by measuring a Limited Oxygen Index (LOI) for the specific materials used to construct the cable. Conventional copper and fiber optic cable designs of data grade telecommunication cables for installations in plenum chambers employ a halogenated low smoke polyvinylchloride (PVC) generating jacket material. For example, a conventional design may include a filled PVC formulation or a fluoropolymer material surrounding a core of twisted conductor pairs, with each conductor individually insulated with a fluorinated-based insulation (e.g., fluorinated ethylene propylene (FEP)).
Recently, the development of “high-end” Category 6 and 7 cables has increased the need for fluorinated ethylene propylene (FEP), perfluoroalkoxy (PFA) and perfluoromethylalkoxy (MFA) that include power sum near end crosstalk (“NEXT”) and power sum equal level far end crosstalk (“ELFEXT”) considerations along with attenuation, impedance, and attenuation crosstalk ratio (“ACR”) values in design of such cables.
Recent and proposed cable standards are increasing maximum frequencies supported by the cables from 100-200 MHz to 250-1000 MHz Recently, 30 Gbits of data over copper high-speed standards have been proposed. The maximum upper frequency of a cable is that frequency at which the attenuation/cross-talk ratio (“ACR”) is approximately equal to 1. Since signal strength decreases with frequency data attenuation and cross-talk increases with frequency, the design of cables that would support high frequencies poses a significant challenge. This is especially true since many conventional designs for cable components, e.g., fillers and spacers, may not provide sufficient cross-talk isolation at the higher frequencies.
The selection of materials for forming cables that can support high frequencies and concurrently exhibit favorable flame and smoke characteristics can be challenging. Fluorinated ethylene/propylene polymers traditionally exhibit better electrical performance comparable to non-halogenated polyolefin polymers, such as polyethylene or polypropylene. Polyethylene has favorable mechanical properties as a cable jacket due to its tensile strength and elongation to break. However, polyethylene exhibits unfavorable flame and smoke characteristics.
Limiting Oxygen Index (ASTM D-2863) (“LOI”) is a test to determine the percent concentration of oxygen that will support flaming combustion of a test material. The greater the LOI, the less susceptible a material is to burning. In the atmosphere, there is approximately 21% oxygen, so a material exhibiting an LOI of 22% or more cannot burn under ambient conditions. As pure polymers without flame retardant additives, members of the polyolefin family, namely, polyethylene and polypropylene, have an LOI of approximately 19. Because of their LOI, these polyolefins exhibit disadvantageous properties relative to flame retardancy in that they do not self-extinguish a flame, but rather propagate a flame with a high rate of heat release. Moreover, the burning melt can spread and drip on surrounding areas, thereby further propagating the flame. These materials could burn similarly to kerosene or gasoline when ignited which is unacceptable for use in building plenum areas.
Table 3 below summarizes the electrical performance and flame retardancy characteristics of several conventional polymeric materials. Besides fluorinated ethylene/propylene, other commercially used melt extrudable thermoplastics generally do not provide a favorable balance of properties (i.e., high LOI, low dielectric constant, and low dissipation factor). Moreover, when flame retardant and smoke suppressant additives are included within such thermoplastic materials, the overall electrical properties generally deteriorate.
TABLE 3Fire Retardancy Characteristics for Copper Cabling and Fiber OpticLAN CablesElectrical PropertiesDielectricDissipationConstantFactorMaterial Type*1 MHz,1 MHz,(Flame Retardant Used)23° C.23° C.LOI %**PE (No Halogen)2.20.000319FRPE (Brominated)2.6-3.00.00328-32FEP (Fluorinated)2.10.0003>90 PVC (Chlorinated)2.7-3.50.02432RSFRPVC (Chlorinated) Reduced3.2-3.60.01839Smoke Fire RetardantLSFRPVC (Chlorinated)3.5-3.80.038-0.08049Low Smoke Fire Retardant*PE = polyethylene; FRPE = flame resistant polyethylene; FEP = fluorinated ethylene-propylene; PVC = polyvinyl chloride; RSFRPVC = reduced smoke flame retardant polyvinyl chloride; LSFRPVC = low smoke flame retardant polyvinyl chloride**LOI = Limiting Oxygen Index
In addition to the requirement of low smoke evolution and flame retardancy for plenum cables, there is a growing need for enhanced electrical properties for the transmission of voice and data over twisted pair cables. In this regard, standards for electrical performance of twisted pair cables are set forth in the Telecommunications Industry Association (TIA) and American National Standards Institute (ANSI) in ANSI/TIA-568-C.2. Similarly, the standards for data transmission over optical fiber cables are covered in ANSI/TIA-568-C.3.
A balance of properties or attributes is needed for each component (e.g., insulation, buffer, cable fillers, fiber optic strength member, fiber optic blown tubing and jacketing) within copper and fiber communications cable so that it can meet the electrical performance of copper cabling or the transmission characteristics of fiber optic high speed data cable and pass the NFPA 262 Flame and Smoke Requirements, the NFPA 259 flame requirements and similarly the European standards for Class B and Class C.
Optical fiber cables exhibit a set of needs that include unique mechanical properties to prevent damage to the fragile glass fibers. These needs are evolving for hybrid copper and fiber designs, Passive Optical Networks (PON) or Power over Ethernet (PoE). For instance, PoE will generate more heat as it provides data transmission as well as power to LED lighting, wireless interface points, cameras and is employed in a wide range of other applications whereby temperature control systems and office automation will be accomplished remotely from interactive phones and computer devices. These cables will require higher temperature rated polymers, e.g., 125° C. to 250° C. operating use temperatures. A direct current with up to 51 watts can be used over a single 4-pair cable if all 4 pairs of the category 5, 5e, 6 and 6A are energized.
Power Over Ethernet (POE) relates to a system in which electrical power can pass safely along with data on these Ethernet cables. IEEE 802.3 af-2003 standard provides up to 15.4 watts of DC power and can operate with Category 3 cables at this low power requirement. IEEE 802.3 at-2009 standard also known as POE+ or POE plus provides 25.5 watts of power over Category 5 or higher with some vendors announcing that up to 51 watts of power could be transmitted with higher temperature performance polymers as the insulation.
There remains a need for a communications cable that can operate reliably while minimizing or eliminating cross-talk between conductors within a cable or alien cross-talk between cables, and also a need for separators for use in such telecommunications cables, while meeting the design criteria described above, such as having a temperature rating up to 200° C. or even 250° C. There also remains a need for a communications cable that can provide low smoke generation and overall flame retardancy, e.g., as required by the NEC for use in plenum and riser areas of a building. Further, despite advances in fabricating polymeric foamed articles for use in cable design, there is still a need for improved foamable and foamed compositions, and methods of their fabrication, for use in cables, e.g., telecommunications cables.